In recent years, a method of creating radiation images has been utilized employing a radiation image conversion panel possessing a stimulable phosphor.
It is a process of employing a radiation image conversion panel possessing a stimulable phosphor layer provided on a support as disclosed in the U.S. Pat. No. 3,859,527 and Japanese Patent O.P.I. Publication No. 55-12144, for example. A stimulable phosphor layer in the radiation image conversion panel is exposed to the radiation passing through an object, so as to store radiation energy corresponding to the radiation transmittance of each portion of the object to form a latent image (stored image), the radiation energy stored at each portion is radiated by scanning this stimulable phosphor layer by stimulated emission light (laser light used in this case) to be converted into light, and the strong or weak light intensity is read to obtain an image. This image may be reproduced on various kinds of displays such as a CRT and so forth, or may be reproduced as a printed copy.
It is demanded that a stimulable phosphor layer in a radiation image conversion panel utilized in this radiation image conversion method exhibits high radiation absorptance and light conversion efficiency, together with excellent graininess of an image and high sharpness.
In order to improve radiation sensitivity, it is preferred commonly to make the stimulable phosphor layer thicker.
The thinner the stimulable phosphor layer is, the higher the sensitivity, but the sensitivity drops largely if the layer is too thin.
Since graininess of an image depends on location-fluctuation of the radiation quantum number (quantum mottles), structure-fluctuation (structure mottles) of a stimulable phosphor layer in a radiation image conversion panel or such, images are deteriorated by increasing quantum mottles via reduction of the radiation quantum number absorbed in the stimulable phosphor layer when the layer becomes thinner, or increasing structure mottles via elicitation of the structure-fluctuation. Accordingly, it was desired that the thick stimulable phosphor layer was used in order to improve graininess of an image.
The image quality and sensitivity in the radiation image conversion method employing a radiation image conversion panel are determined through various factors as described above. Though various studies and trials to improve these image quality and sensitivity have intensively been done by adjusting plural factors relating to them, still not much satisfactory outcome has been obtained.
On the other hand, there were problems to be improved in view of preparation of a radiation image conversion panel. In order to have a stimulable phosphor provided on a support, a vapor deposition method has been utilized in recent years in place of a conventional coating method, since a coating material contains components making no contribution to luminescence such as binder and so forth. It has been known, however, that burr generated at support ends of the radiation image conversion panel deteriorates a moisture resistance property, resulting in degradation of a moisture resistance film, and also causes a problem when a support cut in a panel size in advance is used.
A stimulable phosphor usable in a radiation image conversion panel generally exhibits a large moisture absorption property, and is deteriorated as time passes, since moisture in the air is absorbed in the case of standing in a room under the regular climate condition. When a stimulable phosphor is placed at high humidity, for example, radiation sensitivity of the foregoing phosphor drops with increase of absorbed moisture. Generally, a latent image of a radiation image recorded in a stimulable phosphor is also regressed as time passes after radiation exposure. Thus, the regressing speed of the foregoing latent image becomes large as the stimulable phosphor absorbs moisture, though there exists a characteristic in which intensity of a reproduced radiation image signal becomes smaller with a longer time from radiation exposure to scanning by stimulating light. Therefore, reproduction of a reproduced signal during reading the radiation image drops in the case of employing a radiation image conversion panel possessing a moisture-absorbed stimulable phosphor.
Further, in the case of forming a stimulable phosphor layer on a support inside a vacuum apparatus by an evaporation method and the like, it has been a problem to be solved to improve production efficiency of a radiation image conversion panel, since a ratio of the crystal-formed amount adhering to a support, based on the phosphor amount evaporated from a crucible is as small as 3-10%. Particularly, in order to prepare several sizes of radiation image conversion panels efficiently, a stimulable phosphor layer was formed on a support having the area where a plurality of radiation image conversion panels can be occupied. Subsequently, each of radiation image conversion panels was cut in a desired dimensional size employing laser cutting, punching or another technique to prepare a plurality of radiation image conversion panels. In the case of preparation employing these techniques, the similar problem caused by burr appeared.
When a radiation image conversion plate (a plate having a phosphor layer provided on a support) was tried to be cut by shirring or such, there was a problem such that the plate was deformed, and the phosphor layer was peeled from the support, and there was another problem such that high burr was generated during cutting. In the case of the burr being too high (in the case of average height of burr exceeding 400 μm), when the direction in which burr is generated is vertical to the panel surface and is on the phosphor layer side, images are deteriorated because of peeling of the phosphor layer, and when the direction is opposite (the direction in which burr is generated is vertical to the panel surface and is on the support side), a moisture resistance film to moisture-prevent a radiation image conversion panel is deteriorated. These are not preferable.
Further, it is not preferable that a cutting speed when using a diamond cutter is slow, and electrolyte is also used in the case of employing a cutting process such as electrostatic processing and so forth.
After forming a recording layer (a magnetic recording layer, an optical recording layer, or a magneto-optic recording layer) and a protective layer provided on a large support, a method of preparing a plurality of recording media by cutting these layers via laser cutting, electrical discharge machining or machining is disclosed in Patent Document 1, but it is not associated with radiation image conversions.
(Patent Document 1) Japanese Patent O.P.I. Publication No. 5-128509